1. Field of the Invention
The present invention relates to an electromagnetic noise measurement apparatus, an electromagnetic noise measurement method and a recording medium. More particularly, the present invention relates to an electromagnetic noise measurement apparatus and an electromagnetic noise measurement method for measuring electromagnetic noise radiated from electronic equipment, as well as a recording medium.
2. Description of the Related Art
Recently, as electric equipment and electronic equipment spreads, electromagnetic interference becomes an object of social concern. To deal with this problem, a standard (VCCI or FCC) is set in each country. It is required to satisfy these standards when apparatuses are put on the market.
To judge whether or not electric equipment or electronic equipment conforms to an EMI standard, it is necessary to measure electromagnetic noise radiated from the equipment and to check if a measurement value is below a standard value. The electromagnetic noise measurement is usually made in a range of 30 MHz to 1 GHz.
A determination as to whether a product conforms to the EMI standard is made based on the result of a quasi-peak measurement. This quasi-peak measurement requires fixed measurement time, and measurement efficiency deteriorates if the measurement is made in a range of 30 MHz to 1 GHz. For these reasons, the quasi-peak measurement method is not popular.
At an ordinary electromagnetic wave measurement facility (open field test site or the like), a peak is measured by using a spectrum analyzer instead of executing a quasi-peak measurement in a regulated frequency range. During the measurement, it is checked whether or not this peak conforms to a corresponding standard value. As for an interference signal which does not have a sufficient margin of allowable values, a quasi-peak is measured.
In order to measure the maximum value of electromagnetic waves radiated from an apparatus such as electric equipment or electronic equipment, such a measurement facility further requires a means for turning the measurement target apparatus (apparatus to be measured) and a means for elevating an antenna which receives electromagnetic waves radiated from the measurement-target apparatus.
Further, if conventional automatic electromagnetic wave measurement software is employed, the electromagnetic noise of an apparatus is measured while a reception antenna is fixed to a predetermined position based on a calculation formula using an antenna, which formula is referred to as a height pattern, or on an actual measurement value obtained by using a transmission-reception antenna, so as to efficiently carry out the software operation.
However, if an electromagnetic interference wave has a high directivity toward the height direction of the antenna and electromagnetic waves are measured with the antenna set at a fixed height, the electromagnetic interference wave which should be measured sometimes cannot be measured.
An electromagnetic wave measurement apparatus used at the above-stated electromagnetic wave measurement facility is constituted by connecting, with coaxial cables or the like, an antenna for receiving electromagnetic interference waves generated respectively from electric equipment and electronic equipment, an amplifier amplifying the respective electromagnetic waves received by the antenna, a spectrum analysis means for displaying the results of the received electromagnetic waves, a field intensity meter and the like. To check whether or not the electromagnetic interference waves are below a standard value, it has been necessary that electromagnetic interference wave input and output gains and losses (factors) on the respective parts are calculated, and the calculated factors are offset from the electromagnetic waves received on the respective parts to thereby check that each measurement value is less than the standard value. In addition, no consideration has been given to electromagnetic noise signal generation timing which differs according to measurement target apparatuses and to temporarily observed noise.
Moreover, these gains and losses have been measured and managed at a predetermined signal level which is greatly different from the levels of electromagnetic noises emitted from the actual measurement target apparatuses. In this case, output linearity relative to changes in the magnitude of inputs is not examined. While a factor with respect to a certain input is precise, a factor with respect to variable inputs tends to be imprecise, with the result that measurement values cannot be often compared with the standard value.
Meanwhile, according to the standard regarding the above-stated electromagnetic noise, it is required to measure a QP (quasi-peak) and to judge whether or not this Qp measurement value satisfies a standard value. With the above-stated electromagnetic interference evaluation method, radiated noise is measured, electromagnetic wave levels with various frequencies are respectively measured, electromagnetic wave levels corresponding to the harmonic components of a specific repetition signal among a plurality of repetition signals of the apparatus are automatically extracted from the measurement results and a QP measurement is automatically made. If the respective harmonic components of the specific repetition signal overlap those of a different repetition signal with the same frequency or if the harmonic components of the specific repetition signal are adjacent to those of the different repetition signal, the automatic QP measurement of a measurement target harmonic may sometimes cause an error.
Further, if a measurement system receives a signal having an equivalent intensity for the level of electromagnetic noise radiated from a measurement target apparatus, the measurement system does not always exhibit linearity performance and errors may possibly occur to a measurement result.
The present invention has been made to solve the above-stated disadvantages. It is, therefore, an object of the present invention to provide an electromagnetic noise measurement apparatus, an electromagnetic noise measurement method and a recording medium, which are capable of preventing erroneous measurement of electromagnetic noise and of enhancing measurement efficiency.
To achieve the above object, a first aspect of the present invention is an electromagnetic noise measurement apparatus for measuring electromagnetic noise radiated from an equipment to be measured, the apparatus including: an antenna for receiving the electromagnetic noise; a peak field intensity measuring section which receives the electromagnetic noise from the antenna and measures a peak field intensity of the electromagnetic noise in a predetermined frequency range; a quasi-peak measuring section which receives the electromagnetic noise from the antenna and measures a quasi-peak of the electromagnetic noise at a specific frequency determined in advance; and an informing section which receives measurement results from the peak field intensity measuring section and the quasi-peak measuring section, and, if a difference between a peak field intensity value at the specific frequency and a quasi-peak value at the specific frequency are equal to or more than a predetermined value, informs a predetermined message.
According to this invention, electromagnetic noise radiated from, for example, an electronic equipment (the equipment to be measured) such as, a printer, a copying machine or a facsimile machine or the like, is received by the antenna. When the antenna is to receive the electromagnetic noise, the antenna is moved by an antenna elevating section which elevates the antenna to, for example, a position at which electromagnetic noise is maximized, the electronic equipment is put on a turn table and the electromagnetic noise is received while the turn table turns.
The peak field intensity measuring section measures the peak field intensity of the electromagnetic noise received by this antenna in a predetermined frequency range. For the peak field intensity measuring section, a well-known spectrum analyzer, for example, can be used.
The quasi -peak measuring section measures the quasi -peak, i.e., QP value, of the electromagnetic noise received by the antenna at a preset frequency (a specific frequency determined in advance). For the quasi-peak measuring section, a well-known field intensity meter (receiver), for example, can be used. The preset frequency refers to, for example, a frequency of the electromagnetic noise at which the peak field intensity exceeds a predetermined threshold value. A setting section may be also provided, at which the specific frequency for the quasi-peak measuring section may be set on the basis of peak field intensity of the electromagnetic noise measured by the peak field intensity measuring section and the predetermined frequency range. This setting may be made manually by an operator or automatically by automatic detection of frequencies of the electromagnetic noise which exceed the predetermined threshold of the peak field intensity.
Meanwhile, in the QP measurement, a sharp peak waveform which does not continue for a predetermined duration specified by a standard cannot be measured. As a result, if measurement conditions of the peak field intensity measuring section and the quasi-peak measuring section differ for some reason, there is a possibility that a value measured by the quasi-peak measuring section while automatically measuring the QP value is not correct, which situation will cause erroneous measurement.
Considering the above, the informing section informs by, for example, displaying an error message indicating that the measurement should be made manually on the display section, in a case where the difference between the peak field intensity and the quasi-peak is equal to or greater than a predetermined value at the specific frequency. Consequently, it is possible to prevent erroneous measurement even if the QP measurement is made automatically.
Clock frequencies of clocks (clock devices) mounted on respective substrates of the electronic equipment may be stored in a storage section in advance as a clock list. A waveform at a frequency of an integer multiple of a clock selected from this clock list, i.e., a harmonic waveform, may be superposed on a noise waveform of a preset frequency and displayed on the display section. As a result, it is possible to easily specify a clock whose substrate is a noise source.
Further, the display section may display waveforms of a plurality of frequencies, a calculation section may calculate a difference between the waveforms of the plurality of frequencies and the waveform of a preset basic frequency and a calculation result may be stored in a storage section. As a result, it is possible to easily compare a waveform of electromagnetic noise measured at, for example, electronic equipment provided with a substrate for which counter-measures against electromagnetic noise have not been taken yet, with a waveform of electromagnetic noise measured at electronic equipment provided with a substrate for which counter-measures against electromagnetic noise have been taken. Further, the electromagnetic noise on the substrate may be assigned different colors according to levels and displayed in a three-dimensional style.
Further, to achieve the above object, a second aspect of the present invention is an electromagnetic noise measurement method for measuring electromagnetic noise radiated from an equipment to be measured, the method including the steps of: receiving the electromagnetic noise by an antenna; measuring a peak field intensity of the electromagnetic noise received by the antenna in a predetermined frequency range; measuring a quasi-peak of the electromagnetic noise received by the antenna at a specific frequency determined in advance; and informing a predetermined message if a difference between a peak field intensity value at the specific frequency and a quasi-peak value at the specific frequency are equal or more than a predetermined value. Accordingly, it is possible to prevent erroneous measurement of the electromagnetic noise.
Furthermore, to achieve the above object, a third aspect of the present invention is a computer-readable recording medium at which is recorded a program for controlling measurement of electromagnetic noise radiated from an equipment to be measured, wherein the program causes a computer to execute a process including the steps of: receiving the electromagnetic noise by an antenna; measuring a peak field intensity of the electromagnetic noise received by the antenna in a predetermined frequency range; measuring a quasi-peak of the electromagnetic noise received by the antenna at a specific frequency determined in advance; and informing a predetermined message if a difference between a peak field intensity value at the specific frequency and a quasi-peak value at the specific frequency are equal or more than a predetermined value. Accordingly, it is possible to prevent erroneous measurement of the electromagnetic noise.
To achieve the above object, a fourth aspect of the present invention is an electromagnetic noise measurement apparatus for measuring electromagnetic noise radiated from an equipment to be measured, the apparatus including: a signal generating section for generating a signal corresponding to the electromagnetic noise; a plurality of processing sections connected in series, for being inputted the signal from the signal generating section and for performing predetermined processes; a comparing section for comparing a field intensity level of the signal outputted from the signal generating section with at least one of processed signals which are processed by the plurality of processing sections; and a display section for displaying a comparison result of the comparing section.
According to the fourth aspect, the signal generating section generates a signal which replaces the electromagnetic noise radiated from the equipment to be measured (for example, an electronic equipment). This signal is inputted into a plurality of processing sections connected in series, e.g., an amplifier for amplifying a signal received by the antenna and a spectrum analyzer, or the amplifier and a field intensity meter, and processed therein.
The processing sections mentioned above individually have linear input and output characteristics. However, there are cases where, if these sections are connected in series and regarded as a single processing section, linear input and output characteristics cannot be obtained.
In view of the above, the comparing section compares the field intensity level of the signal outputted from the signal generating means with that of the signal which has been processed by the plurality of processing means, and the comparison result is displayed on the display section. As a result, it is possible to easily check the linearity of the plurality of processing sections for measuring the electromagnetic noise. It is, therefore, possible to accurately measure the electromagnetic noise.